1. Field of the Invention
The present invention relates to a check valve. The check valve is suitable for use in a refrigerating circuit having a variable capacity type compressor or in the compressor itself. In particular, the check valve is useful to realize a discharge capacity of substantially 0%, in the case where the compressor is operatively coupled to an external drive source in a clutchless manner.
2. Description of the Related Art
A compressor is incorporated in, for example, a refrigerating circuit used for a car air-conditioning system to compress the coolant gas. Such a compressor is usually operatively coupled to a car engine, as an external drive source, via a magnetic clutch by which the compressor is connected to the engine only when a refrigerating load occurs to effect a compressing operation. However, if the magnetic clutch is provided in the compressor, problems arise in that a total weight increases, a production cost increases, and a power is consumed for operating the magnetic clutch. To eliminate such a drawback, there has recently been a proposal of a so-called clutchless swash plate type variable capacity type compressor which is directly coupled to an external drive source without a magnetic clutch interposed between the engine and the compressor, so that the compressor is normally driven while the external drive source is operating (for example, refer to Japanese Unexamined Patent Publication (Kokai) No. 10-205446).
In the compressor disclosed in the above-described publication, a swash plate is arranged so that it is tiltable with respect to a drive shaft directly coupled to the external drive source, and a minimum tilting angle of the swash plate is maintained to provide a discharge capacity which is not zero %. Therefore, in this compressor, it is possible to realize reduction of weight as well as to minimize power consumption of the external drive source, by directly coupling the compressor to the drive source without a magnetic clutch.
Also, a check valve is arranged in this compressor, as shown in FIG. 14 of the attached drawings. That is, a housing 90 has a discharge chamber 91, an accommodation chamber 92 adjacent to the discharge chamber 91 and an outer discharge passage 93 for fluid communication between the accommodation chamber 92 and a condenser (not shown) of a refrigerating circuit, and a check valve 94 together with an O-ring 95 and a circlip 96 is arranged in the accommodation chamber 92 to prevent a coolant gas from reversely flowing into the accommodation chamber 92. More specifically, the check valve 94 comprises a valve seat member 81, a case 82 fitted to the valve seat member 81, a valve element 83 axially slidably arranged in the case 82, and a spring 84 for biasing the valve element 83 toward the valve seat member 81 in the case 82, as shown in FIGS. 15 and 16.
A flow passage 81a is formed through the valve seat member 81 in communication, on one hand, with the discharge chamber 91 and, on the other hand, with the interior of the case 82, and a valve seat 81b is formed in the valve seat member 81 around the outlet of the flow passage 81a. Also, an annular groove 81c is provided in the outer peripheral surface of the valve seat member 81 around the valve seat 81b. 
Projections 82a are formed in the inner wall of the open-side end of the case 82 to fit in the annular groove 81c, and communication holes 82b are formed in the outer peripheral wall of the case 82 on the axially opposite side of beyond the valve seat 81b. 
The valve element 83 has a seal surface 83a, which is in contact with the valve seat 81b when the valve element 83 slides in one direction toward the valve seat 81b and leaves the valve seat 81b when it slides in the other direction, and an outer peripheral surface 83b perpendicular to the seal surface 83a. 
As shown in FIG. 15, in this check valve 94, when the compressor is stopped due to the stopping of the external drive source, a high pressure coolant gas on the side of the condenser and the biasing force of the spring 84 are applied to the valve element 83 to cause the latter to slide in the one direction. Thus, the seal surface 83a is seated on the valve seat 81b of the valve seat member 81 to disconnect the flow passage 81a from the communication holes 82b. Accordingly, the high pressure coolant gas on the side of the condenser is prevented from reversely flowing into the discharge chamber 91.
On the other hand, as shown in FIG. 16, during the operation of the compressor, the high pressure coolant gas in the discharge chamber 91 pushes the valve element 83 through the flow passage 81a, and overcomes the biasing force of the spring 84 to cause the valve element 83 to slide in the other direction. Accordingly, the seal surface 83a leaves the valve seat 81a of the valve seat member 81 to allow the flow passage 82b to be connected to the communication holes 82b. Thus, the high pressure coolant gas in the discharge chamber 91 is delivered to the condenser.
Therefore, in the compressor with such a check valve 94, it is possible to prevent the coolant gas from reversely flowing when the compressor is stopped, so it is possible to prevent the liquid coolant from being held in the compressor and to avoid an excessive temperature or pressure rise in the compressor, as well as to improve durability of the compressor.
Also, in the compressor having a flow passage extending from the discharge chamber 91 to the crank chamber (not shown), it is possible to suppress the pressure rise in the crank chamber when the compressor is stopped, which allows a quick increase in the tilting angle of the swash plate and a quick recovery of the high capacity condition upon starting the operation of the compressor, resulting in a rapid appearance of the refrigerating effect.
However, according to the experimental result considered by the inventors of the present case, it has been found that a pressure loss is apt to occur soon after the check valve is opened by the movement of the valve element 83 away from the valve seat 81b and the flow passage 81a starts to communicate with the communication holes 82b, since in this check valve 94, the case 82 and the valve element 83 are made as plastic molded products to reduce the manufacturing cost and the weight, and the outer peripheral surface 83b of the valve element 83 perpendicularly extending from the seal surface 83a thereof is formed in a simple cylindrical shape.
That is, the case 82 and the valve element 83 as resin molded products form a relatively large clearance between them since tolerances are required. As shown in FIG. 17A, when the valve, in which the valve element 83 is seated on the valve seat 81b, is fully closed, a fluid such as a coolant gas will not leak from the flow passage 81a even if the outer peripheral surface 83b of the valve element 83 is formed in a simple cylindrical shape, since the outlet opening of the flow passage 81a is closed by the seal surface 83a. Also, as shown in FIG. 17C, when the valve, in which the valve element 83 is lifted to the top dead center, is fully opened, there is no problem occurring due to an increase in the back pressure behind the valve element 83, since the fluid flows out from the flow passage 81a to the exterior of the case 82 via the largely opened communication hole 82b rather flowing into a gap between the inner peripheral surface of the case 82 and the outer peripheral surface 83b of the valve element 83. However, as shown in FIG. 17B, when the valve is at an initial stage of opening in which the valve element 83 slightly leaves the valve seat 81b, the fluid which flows out from the flow passage 81a passes through the clearance between the inner peripheral surface of the case 82 and the outer peripheral surface 83b of the valve element 83 to the back side of the valve element 83 in the simple cylindrical shape. Therefore, the back pressure behind the valve element 83 increase and the sliding movement of the valve element 83 in the opening direction is prevented. In this case, the pressure difference by which the valve element 83 is lifted becomes higher and a pressure loss occurs in the check valve 94 itself.
Especially, in the case where the check valve 94 is provided on the side of the condenser in the refrigerating circuit or on the downstream side of the discharge chamber 91 of the compressor, the pressure in the flow passage 81a is high, and the pressure loss adversely affects the refrigerating circuit and a car having such a refrigerating circuit mounted.
It is desirable to equip the above-mentioned check valve 94 in the compressor operatively coupled to the external drive source in a clutchless manner in order to obtain the above-mentioned operation and effect, but such an advantageous operation and effect might be cancelled if there is an inconvenience such as pressure loss in the check valve 94.
In view of the above described prior art problems, an object of the present invention is to provide a check valve which can reduce the pressure loss after the valve opens.
Another object of the present invention is to provide a refrigerating circuit and a compressor having such a check valve in which the pressure loss in the compressor and the refrigerating circuit can be reduced, and drawbacks caused thereby are eliminated.
The present invention provides a check valve which comprises a valve housing having a peripheral wall, a flow passage with an inlet opening and an outlet opening formed in the peripheral wall, a valve seat formed in the peripheral wall around the outlet opening, and a communication hole formed through said peripheral wall on the axially opposite side of the valve seat from the flow passage; a valve element having an outer wall axially slidably arranged in the peripheral wall of the valve housing, and a seal surface engagable with the valve seat; and an urging member for biasing the valve element toward the valve seat. The check valve is characterized in that it comprises a guide means for guiding a fluid, which leaks from the outlet opening of the flow passage into the interior of the valve housing past the seal surface when the valve element leaves the valve seat, to the outside of the valve housing.
In the check valve according to the present invention, when the valve is at an initial stage of opening in which the valve element slightly leaves the valve seat, the guide means guides the fluid, which leaks from the outlet opening of the flow passage into the interior of the valve housing along the seal surface, to the outside of the valve housing. Therefore, the flow of the fluid toward the back side of the valve element is prevented, and the increase in the back pressure behind the valve element is prevented, so the sliding movement of the valve element in the opening direction is assured. Thus, the pressure difference by which the valve element is lifted will not become higher and a pressure loss in the check valve itself is reduced.
Preferably, the guide means comprises a guide passage formed in the valve element such that the guide passage is communicated with the communication hole when the valve element leaves the valve seat.
In the case where the valve element is made as a resin molded product, a relatively large clearance exists between the valve element and the valve housing. However, the present check valve worked well in when such a large clearance existed. It is easy to form a groove in the outer circumferential surface of the outer wall of the valve element. In this case, preferably, the groove is formed annularly in the outer surface of the outer wall of the valve element over the entire circumference thereof, since the groove is normally connected to the communication hole irrespective of angular positions of the valve element.
Preferably, the valve housing comprises a first housing member having the flow passage and the valve seat, and a second housing member coaxially coupled to the first housing member and having the communication hole, the first and second housing members together forming the peripheral wall of the valve housing, the valve element and the urging member being arranged in the second housing member. If the valve housing is constituted by separate members in this way, the manufacture of the check valve at a lower cost is facilitated. Preferably, the second housing member is generally cup shaped.
The check valve of the present invention is suitably used in a refrigerating circuit having a condenser and a variable displacement compressor with a discharge chamber communicating with the condenser. Particularly, it is more effective if the communication hole communicates with the condenser.
Preferably, the check valve is incorporated in the variable displacement compressor, rather than it is arranged in the piping of the cooling circuit. The coolant gas may expand in the piping on the upstream side of the check valve and reversely flow into the compressor, if the check valve is arranged midway in the piping of the cooling circuit, but there is no such problem if the check valve is incorporated in the compressor.
The check valve according to the present invention is especially effective when it is used with a variable capacity type compressor which is operatively coupled to an external drive source in a clutchless manner. In this case, it is possible to prevent the liquid coolant from being accumulated in the compressor and to avoid an excessive rise in temperature and pressure in the compressor, resulting in the improvement in durability of the compressor. Also, this arrangement functions to quickly increase the tilting angle of a swash plate and to quick recover the high capacity condition upon starting the operation. Thus, the refrigerating effect is quickly ensured.
Particularly, this arrangement is advantageous in the case where the variable capacity type compressor is of a type capable of realizing a discharge capacity of substantially 0%. In this connection, the compressor of a type capable of realizing a discharge capacity of substantially 0% is, for example, one in that a minimum tilting angle of the swash plate is selected at a value smaller than a critical angle at which the recovery of the tilting angle of the swash plate is ensured by the reaction of the discharge pressure, as disclosed in EP 0 953 765 A2.